On Some Interactions of Organisms. 13 



otherwise decimate them, ])y simply passing to another 

 more favorable one, without the loss of a life, fit them, 

 above all other animals and agencies, to arrest disorder at 

 the start, — to head off aspiring and destructive rebellion 

 before it has had time fairly to make head. But we should 

 not therefrom derive the general, but false and mischievous, 

 notion, that the indefinite multiplication of either birds 

 or predaceous insects is good. Too many of either is nearly 

 or quite as harmful as too few. 



And this brings us to tlie application of these principles 

 to the interests of civilized man. We must note how the 

 new forces which he brings into the field expend themselves 

 among those we have been studying, and to what reactions 

 they are in turn subjected. We must first see how far the 

 primitive natural order of life lends itself to the supply 

 of man's needs, to the accomplishment of his purposes ; 

 and must determine, in a general way, where he may be 

 content to leave it undisturbed, where he should address 

 himself to its improvement, and where he is compelled to 

 attempt wholly to set it aside, substituting artificial ar- 

 rangements of his own, devised solely in his own interest. 



Some of Nature's arrangements man finds himself una- 

 ble to improve upon for his own benefit. No one thinks 

 of cultivating the forest to hasten the growth of the wood, 

 or of trimming the wild oak or the maple, or of planting 

 artificially the nuts and acorns in the woods to increase 

 the number of the trees. 



We are content to leave things there to go on essentially 

 in the old way, merely anticipating the processes of nat- 

 ural death and decay by removing the trees before they 

 spontaneously j)erish, and glad if the revolutions of organic 

 life which we set up in the country around do not pene- 

 trate to the forest, visiting the leaves and trunks of the 

 trees with the scourge of excessive insect depredations. 



Usually, however, we find the ready-made system of 

 Nature less to our liking, and all our cultures are attempts 

 to set it aside more or less completely. In the pasture and 

 meadow, it answers our purpose to substitute other species 

 for the grasses growing there spontaneously, and these 

 adapt themselves easily to the circumstances which have 



